Locals in the Melbourne outer south-western suburb of Werribee describe the Ballan Road as a 'death trap.'
One driver was killed and another injured on the road on June 14, when a hatchback travelling north swerved and collided with an oncoming Falcon.
Road shoulders, residents assert, have been deteriorating as a result of weather, heavy vehicles and insufficient maintenance. As well as having poor lighting, the road is full of potholes.
Such incidents underscore the importance of effective road maintenance. In Victoria alone, around 1,452 kilometres of road were ‘distressed’ according to the Victorian state government budget papers (2015/16) – equivalent to 7.4 per cent of road surface across the state. In some areas, things are worse. Corangamite Shire in the south-west says its roads are 18 per cent distressed.
This matters. When braking at low speeds, roughness in road surfaces can reduce the degree of friction between the tyre and the road by up to 80 per cent, a 2012 study has found. This increases stopping distances and the risk of crashing. An earlier study in 1998 found that each unit of improvement in road surface under what is known as the International Roughness Index improved vehicle rolling resistance by between three and six per cent. Potholes add to hazards as vehicles swerve or deviate to avoid them.
Roughness also affects surface drainage, ride comfort, dynamic loading, the condition of vehicles (through increased wear of parts) and vehicle emissions efficiency. In the US, the National Asphalt Pavement Association estimates that a maintenance program which slightly increases smoothness can reduce annual vehicle fuel consumption by as much as 7 billion gallons each year – equivalent to taking 10 million vehicles off the road for a year in that country.
The importance of effective maintenance is further increased given the amount of taxpayer money spent on it. Victoria, for instance, is spending $500 million on the maintenance of existing roads in 2017/18. Queensland in 2016/17 spent $892 million.
Toward this end, a study published by Austroads in May sought to shed light on the types of treatment which deliver the best outcomes. To do this, it used observational data supplied by Queensland’s Department of Transport and Main Roads, NSW’s Roads and Maritime Service and Victoria’s Vicroads along with performance data from iPave in Queensland and New South Wales. The data related to pavement history, pavement strength, matching traffic data, climate, postal speed limits and nominal levels of service.
The nine treatments tested were asphalt surfacing, emulsion seal, geotechnical seal, microsurfacing, normal reseal, open graded asphalt (OGA), polymer modified binder (PMB) seal, rehabilitation and rejuvenation.
Typically, road pavement performance can be considered in three stages. First, there is the gradual deterioration of the surface following construction. This leads to roughness, rutting and/or cracking. According to the report, this typically lasts about 40 years before the pavement reaches its stage of minimum levels of service (just above 40 per cent) and requires treatment. Immediately following this, performance usually recovers to somewhere around 80 per cent. Finally, the pavement will again deteriorate over something like 30 or 40 years before again falling below minimum levels.
This deterioration is not linear. Immediately following construction or treatment, road surfaces undergo around 20 years of gradual deterioration before subsequently experiencing increasingly rapid deterioration as decreasing pavement strength leads to levels of rutting at increasing rates.
As shown in the study, the rate of deterioration is directly linked to the pavement strength and the traffic load to which the pavement is subject. On pavement strength, the results show that roughness, rutting and cracking all increased as pavement ‘deflection’ (indicating reduced strength) also increased. Roughness also increased with traffic load in respect of most of the treatments tested; rutting and cracking increased with traffic load for some treatments, but not for the majority of treatments. Whilst road surfacing would generally be expected to deteriorate faster in wetter and more humid climates, results shown through this testing were mixed and inconclusive as to whether this does in fact happen.
OGA wins out
Which was the most effective resurfacing activity?
By far and away, open graded asphalt came out at number one. Indeed, pavements treated with OGA recorded the slowest rate of deterioration across each of roughness, cracking and rutting. In NSW, OAG was shown to reduce deterioration due to roughness by 58 per cent and deterioration due to rutting by 61 per cent.
Geotextile seal was ranked next, ranking second in terms of avoiding rutting and third in terms of avoiding roughness – albeit with this treatment performing less well in respect of reducing cracking, where it came in fifth. In Victoria, geotextile seals were shown to reduce roughness and rutting deterioration by 23 per cent and 55 per cent respectively.
Coming in third, asphalt performed well and was shown to decrease roughness and rutting deterioration by 23 per cent and 55 per cent respectively. Asphalt treatments performed fourth, third and fourth best at in respect of each of roughness, cracking and rutting.
Rejuvenation scored well for roughness but was not ranked overall because it did not have deterioration rates for cracking and rutting.
The report acknowledges that OGA’s ranking is probably related to its typical application on high-quality pavement bases.
Nevertheless, the results appear to demonstrate that OGA, geotextile seals and asphalt are effective pavement treatments.
Austroads did not respond to request for comment.
Australia spends billions on road maintenance each year.
To get the best value, and to maximise safety, we must use the best treatments available.